Project Summary As the large majority of tobacco users initiate in adolescence or young adulthood, it is important to characterize patterns of use across this period of development. For both age groups, a rise in the use of alternative tobacco products (e.g., electronic cigarettes, hookah/waterpipes), as well as the use of two or more tobacco products concurrently (e.g., polytobacco use) has been noted. Yet little work has examined how these patterns of single or polytobacco use change from early adolescence into emerging adulthood, and even less work has examined comprehensively the multitude of factors that might predict this change. The proposed project seeks to fill these gaps by using a combination of variable- and person-centered analytic techniques to examine longitudinal patterns of change and associated antecedents from a socio-ecological framework. Using a nationally-representative dataset, the Population Assessment of Tobacco and Health (PATH), this project will a) examine trajectories and related predictors of single tobacco product use from early adolescence (age 12) to emerging adulthood (age 22) using variable-centered latent growth models, b) examine transitions into and out of polytobacco use classes, as well as predictors of these classes, from early adolescence (age 12) to emerging adulthood (age 22) using person-centered latent transition analysis, and c) examine interactions among individual (e.g., motives for use; sensation seeking), interpersonal (e.g., parent modeling and rules), and contextual (e.g., geographic location) factors in predicting trajectories of single tobacco product use and transitions in polytobacco use. These analyses will not only provide crucial information about the emergence and relative stability of different use patterns over time, but also differences between patterns that are protective versus risky based on a consideration of multifaceted and interacting antecedents. Consequently, our proposal addresses the Food and Drug Administration's research priority to ?identify and explain between- persons differences and within-person changes in tobacco use patterns, including?polyuse of tobacco products (i.e., use of multiple products within the same time-period and switching between multiple products)?. In the long-term, this project can inform evidenced-based public health efforts aimed at preventing or ceasing tobacco use in the earliest stages of use.